In many advanced telecommunication systems, for example, such as Fiber World Products, high performance dc/dc power converters with low voltage, high current output are required. Some of the basic requirements for these power converters are:
a) high efficiency;
b) high power density;
c) high reliability;
d) fast dynamic response;
e) low mass density;
f) low EMI (both conducted and radiated);
g) regulated output dc voltage with low ripple; and
h) constant frequency operation.
It is believed that the above features of the converters will significantly enhance overall performance of the system. Consequently, there is likely to be a trend toward use of such converters in the future.
Various topologies of half-bridge resonant converters are studied and compared in IEEE Trans. on Power Electronics, Vol. 3, No. 2, Apr., 1988, pp. 174-182 "A Comparison of Half-Bridge Resonant Converter Topologies" by R. Steigerwald. A half-bridge inverter is coupled with a series, a parallel or a series-parallel resonant circuit and their performances are compared.
In an article by the present inventor, "Performance Comparison of Pulse Width Modulated Resonant Mode dc/dc Converters for Space Applications", IEEE Industry Applications Society Conference Record, Oct., 1989, pp. 1106-1114, full-bridge resonant converters are described.
PWM series-parallel resonant converters are further studied in "Fixed Frequency PWM Series-Parallel Resonant Converter", by A. K. S. Bhat, IEEE Industry Applications Society Conference Record, Oct., 1989, pp. 1115-1121.
U.S. Pat. No. 4,857,822, issued Aug. 15, 1989 in the name of Tabisz et al, describes a zero-voltage-switched multi-resonant converter in which a multi-resonant switch forms three different resonant circuits for improved performance at higher frequencies.
U.S. Pat. No. 4,833,584, issued May 23, 1989 in the name of Divan, on the other hand, teaches a high frequency quasi-resonant current mode static power converter in which the output voltage is controlled by varying the operating frequency. It is therefore not suitable for the application where frequency locking/synchronization is required.
In the above articles, parallel resonant and series-parallel resonant circuits contain only parallel capacitors as their parallel resonant component.